In combustors, in order to achieve acceptable exhaust gas pollutant levels, thorough mixing of fuel with the oxidant, such as, most commonly used, air, is required before the fuel is burnt. In gas turbines with so-called sequential combustion, such as e.g. described in EP 0 718 470 B1, subsequent combustors are provided with partly expanded, still oxygen-rich, flue gas from a preceding turbine, serving as the oxidant. In such gas turbines, and there in particular in the subsequent combustors, the oxidant entering the combustor, that is, partly expanded flue gas, has a temperature in excess of a fuel self-ignition temperature. That is, the fuel will, after a certain ignition delay time, ignite spontaneously. It is thus crucial to achieve a complete and uniform fuel/oxidant mixing within a limited time frame before the fuel ignites.
US 2012/0272659 A1 for instance discloses a fuel injector device having a generally airfoil-like shape, with a trailing edge having an undulating shape across the flow direction, wherein said undulating aerodynamic cross section develops in a streamwise direction from the leading edge to the trailing edge. At the trailing edge, flows having opposite velocity components across the main flow direction meet and intermingle, and develop vortices propagating downstream from the trailing edge, said vortices having a center of rotation essentially at inflection points of the undulating trailing edge. Fuel is injected through fuel injection means arranged at the trailing edge essentially at said inflection points, and, due to the vortices, is intensively admixed with the oxidant.
The internal geometry of this device is, however, highly complex. Multiple plenums for cooling air, carrier air and at least one fuel need to be provided inside the device. Also, means for guiding and discharging the various fluids need to be provided. Thus, such devices need to be assembled form a multitude of individual parts. The assembly is complex, expensive, and restricts the design possibilities.